1. Field of the Invention
This invention relates generally to shear band of a tire that has means for inducing buckling when the tire is subjected to high deformations, and, more specifically, to a tire that has a shear band with at least one membrane that has a reinforcement having predetermined configurations for controlling the buckling behavior of the reinforcement when the membrane is subjected to compressive stress.
2. Description of the Related Art
An emerging field in tire development involves the manufacture and use of non-pneumatic or hybrid tires that do not depend solely on gas to support the tire structurally as these tires are not prone to deflation, which can render standard pneumatic tires inoperable. An example of such a tire is disclosed by U.S. Pat. No. 7,201,194, which is commonly owned by the applicant of the present application. The content of this patent is incorporated herein by reference for all purposes in its entirety. In an exemplary embodiment of the '194 patent, the non-pneumatic tire includes an outer annular shear band and a plurality of web spokes that extend transversely across and radially inward from the annular shear band and are anchored in a wheel or hub.
In certain embodiments, the annular shear band may further comprise a shear layer, at least a first membrane adhered to the radially inward extent of the shear layer and at least a second membrane adhered to the radially outward extent of the shear layer. The membranes may have reinforcing fibers made from steel, aramid or glass fibers or other suitable material that is substantially inextensible that are embedded in an elastomeric coating. The shear layer may include an elastomer that is rubber, polyurethane or any other suitable thermoset or thermoplastic material. The ratio of the extension or young's modulus (Emembrane) of either membrane to the shear modulus (G) of the shear layer is typically at least 100:1 and is sometimes as high as 3000:1 in order for the tire that has the shear band to mimic the performance of a pneumatic tire. For example, in addition to the ability to operate without a required inflation pressure, the invention of U.S. Pat. No. 7,201,194 also provides advantages that include a more uniform ground contact pressure throughout the length of the contact area. Hence, this tire mimics several performances of a pneumatic tire.
FIG. 1 shows such a tire 100 that defines a radial or vertical direction (R, Z), a circumferential or X direction (C, X), and an axial or Y direction (A, Y). The tire 100 comprises a tread 102 that is attached to the outward extent 104 of the spokes 106, which in turn, are connected to a hub or wheel 108 at their inward extent 110 by means known in the art such as by molding spokes between the hub 108 and the tread 102, which have been prepared for suitable bonding to the polyurethane. Alternatively, the tire could have sidewalls that extend from either side of the tread and that attach the tread to the hub using conventional bead interfaces. In use, such a tire works well when it rides on a relatively smooth road surface because the stress and strain that the shear band experiences is acceptably low.
For example, experience has taught that a typical deflection for such a tire used in an urban setting on an electrical urban vehicle is relatively small and can increase the length of the footprint to about 75 mm. However, occasionally a larger deflection is imposed on the tire that increases the length of the footprint to as much as 150 mm such as when the tire encounters a pothole or a curb. Looking at FIG. 1A, the shear band 112, which comprises first and second substantially inextensible membranes 114, 116 that are separated by the shear layer 118, can be deformed during such an event, exerting compressive stresses on the top or second membrane 116, as viewed in this figure, and tensile stresses on the first or bottom membrane 114, as viewed in this figure. When this happens, two possible problems with the shear band may occur.
First, as the top or second membrane 116 becomes highly stressed in compression, it becomes prone to buckling. This can cause strains between the polyurethane, which often constitutes the shear layer 118, and the metal cords, which is often part of the membrane, to be excessive. At such a high strain, the bond between the cords and the polyurethane is broken and the cords will buckle and deform plastically. Second, the contact patch may grow sufficiently long that shear layer 118 may experience excessive shear strain, such as 15%, causing the shear layer to deform an undesirable amount. In either case, the problem is irreversible causing the shear band 112 to no longer function as originally designed.
Accordingly, it is desirable to find a construction for a shear band that can withstand higher imposed deformations and still be able to rebound and work properly. It is especially desirable to find such a construction that helps to prevent the plastic deformation of the shear layer and the cords found within the inextensible membrane of the tire that experiences compression and is prone to buckling when the tire hits an obstruction and a large deflection is imposed on the tire.